1.5 Cracking

Question 1

What is cracking?

Answer 1

The process of breaking down long chain alkanes into more useful shorter chains

Question 2

What kind of cracking is used?

Answer 2

Thermal cracking

A variation of thermal decomposition

Question 3

What does cracking include?

Answer 3

High heat

A catalyst

Question 4

Describe the process of cracking

Answer 4

The long chain molecules are heated
They are vaporised
The vapour passes over a catalyst at a high temperature
The molecules are cracked on the surface of the catalyst

Question 5

What can’t enter the reaction? Why?

Answer 5

Air

Because the oxygen reacts with the hydrogen and carbon to make H2O and CO2

Question 6

What is the name given to the other hydrocarbon made in cracking?

Answer 6

Alkenes

Question 7

What is the formula for an alkene?

Answer 7

C(n)+H(2n)

Question 8

What do alkenes have that alkanes don’t?

Answer 8

At least one double bond

Question 9

What does the double bond make the alkene?

Answer 9

Unsaturated

Question 10

What bonds do alkenes have?

Answer 10

4 carbon bonds
1 hydrogen bond

At least one double bond between carbons

Question 11

What is the chemical test for alkenes?

Answer 11

They will discolour bromine water from orange to colourless because the double bond reacts with the bromine water

Question 12

Name the first 4 alkenes

Answer 12

Ethene
Propene
Butene
Pentene

Question 13

What is polymerisation?

Answer 13

Many monomers join together to make a polymer

Question 14

What is an alkene called in the plastics industry?

Answer 14

A monomer

Question 15

What conditions are needed for polymerisation?

Answer 15

High heat
High pressure
A catalyst

Question 16

What changes in the many monomers to make polymers?

Answer 16

The double bond breaks

Question 17

What does each of the monomers: ethene, propene and styrene become in polymerisation?

Answer 17

Polyethene
Polypropene
Polystyrene

Question 18

What chemical is added to polymers to make them into plastic?

Answer 18

Plasticisers

Question 19

What are the problems with plastic?

Answer 19

Non-biodegradable
Non-renewable
Burning them produces CO2

Question 20

What is a thermoplastic?

Answer 20

A plastic that can be heated and shaped into a new shape as it is melted down

Question 21

What is a thermoset?

Answer 21

A plastic that will not change on heating

Question 22

Example of a thermoset?

Answer 22

PVC pipes

Question 23

What makes a thermoset and a thermoplastic different?

Answer 23

The strength of the bonds between polymers

Question 24

What are biodegradable plastics made from?

Answer 24

Corn starch?

Question 25

What is the advantage of biodegradable plastics?

Answer 25

Break down more easily

Renewable

Question 26

What two ways can ethanol be produced?

Answer 26

Fermentation

Hydration of ethene

Question 27

How do you get ethanol in fermentation?

Answer 27

Sugar -> ethanol + carbon dioxide

Question 28

What are the advantages of fermentation?

Answer 28

Renewable
Uses little energy
Large quantities produced

Question 29

What are the disadvantages of fermentation?

Answer 29

Increases food prices
Slow process
Ethanol needs to be purified in distillation

Question 31

How do you get ethanol from hydration of ethene?

Answer 31

Ethene + steam (+catalyst) -> ethanol

Question 32

What are the advantages of hydration of ethene?

Answer 32

Fast process
Continuous
Very pure ethanol

Question 33

What are the disadvantages of hydration of ethene?

Answer 33

Non-renewable
Uses a lot of energy
High temperatures are needed